1. Field of the Invention
The present invention relates to cannulae used during cardiac surgery and, more particularly, to a double lumen cannula for both delivering cardioplegic fluid to and for aspirating air from the aorta.
2. The Prior Art
Since the early days of cardiac surgery it has been recognized that in order to provide the optimum surgical conditions when operating in or upon the heart, it is necessary to interrupt the normal operation of the heart since it is very difficult to operate while the heart is beating and while blood is flowing through it. Thus, in order to be able to efficiently perform cardiac surgery it is sometimes necessary to use cardiopulmonary-bypass techniques and to isolate the heart from its life-giving blood supply.
It has been found that most deaths occurring after cardiac surgery are due to acute cardiac failure. At first it was believed that the heart was simply beyond repair and that the operation had failed to correct the problem. Later, however, it was discovered that many of these postoperative deaths were due in part to myocardial injury occurring as a direct result of the surgery. A considerable amount of research has been performed to determine the exact cause of these myocardial injuries and the optimum procedures for maintaining myocardial integrity during open heart surgery.
One of the first methods utilized to protect the myocardium during surgery was normothermic perfusion of the empty beating heart. This method was utilized in an effort to maintain the heart, as near as possible, in normal conditions during the surgery. Although this procedure eliminated the problem of blood flow, disection and suturing were still difficult to perform because of the firmness of the myocardium and the beating of the heart. Additionally, it was found that a significant amount of damage still occurred to the myocardium when this procedure was utilized.
A second method which was developed to protect the myocardium was intermittent cardiac ischemia with moderate cardiac hypothermia. This method requires that the entire body be perfused at a temperature of from 28.degree. C. to 32.degree. C., thus slowing all bodily functions, including those of the heart. The heart is fibrillated before aortic cross-clamping to stop the beating. The surgeon can then operate for approximately 15-25 minutes at which time the heart beat needs to be resumed for three to five minutes. This procedure proved to be an inefficient method for performing operations and had many attendant dangers, including the fibrillation of the heart.
A third method which has been utilized is profound hypothermic cardiac ischemia. This method requires that the temperature of the heart be lowered to about 22.degree. C. by the infusion of cooled perfusate and/or by filling the pericardium with a cold saline solution. One of the major disadvantages of this technique is that the heart continues fibrilate, exhasting the stores of substrate, becomes acidotic and with time causes irreversible muscle damage.
A fourth method which has been developed to maintain the myocardium is the infusion of cold cardioplegic fluid to cool and stop the beating of the heart. After the initial infusion, the heart is reperfused approximately every thirty minutes to maintain the cool, dormant state of the heart.
The use of cardioplegic fluids to protect the myocardium has proven to be the most advantageous method of those tested to date. However, there are still many problems which need to be overcome. For example, the injection of cardioplegic fluids into the heart creates an opportunity for air to enter the aorta and subsequently the arteries. Air embolisms can cause severe damage if they are allowed to pass through the arteries to the heart or the brain. Accordingly, it is important that steps be taken to insure that any entrapped air is removed from the aorta.
In the past, this has been accomplished by forming a small incision in the aorta and by inserting a sucker tube connected to a vacuum source. The incision in the aorta through which the sucker tube passes is in addition to the puncture which is necessary for the needle which injects the cardioplegic solution. Accordingly, in the prior art systems it has been necessary to form both an incision and a puncture wound, thus increasing the trauma to the aorta, the amount of time necessary to position the equipment, and the necessity of closing two wounds when the operation is complete.
Accordingly, if the use of cardioplegic fluids is to be the preferred method of maintaining myocardial integrity during open heart surgery, what is needed in the art is a device for the injection of cardioplegic fluids which overcomes these disadvantages.